Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are typically placed in an “ink loader” having a feed chute or channel. A feed mechanism delivers the solid ink sticks through the feed channel to a heater assembly. In some solid ink printers, gravity pulls solid ink sticks through the feed channel to the heater assembly. Typically, a heater plate (“melt plate”) in the heater assembly melts the solid ink impinging on it into a liquid that is delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al.; and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al., the disclosures of which are incorporated herein by reference, describe exemplary systems for using solid ink sticks (“phase change ink sticks”) in a phase change ink printer.
FIG. 1 is a simplified cross-sectional view of a prior art feed channel 20 and one of a plurality of phase change ink sticks 24. The previously known phase change ink sticks 24 have included various top surfaces 28, bottom surfaces 32, side surfaces 36, and side surfaces 40. These surfaces may be complementary or otherwise correspond to ink loader features to support and guide the ink sticks into optimal feed/melt positions. Some horizontal or near horizontal ink loaders have included “lower laterally offset” or “bottom laterally offset” ink stick supports and/or guide rails 44 that are vertically below and laterally offset from the ink stick centers of gravity 47. In addition to substantially supporting the weights of the ink sticks 24, these ink loader structures 44 have also slidably engaged corresponding protruding and/or inset ink stick features 52 to guide the ink sticks 24 to melt plates (not shown) along substantially straight or other prescribed feed paths. As may be understood by viewing the structure shown in FIG. 1, gravity causes the side 40 of the ink stick 24 which is opposite the lower laterally offset feature 44 to lean and slide against the feed channel wall 48.
Ink loaders typically hold many ink sticks at once and each individual ink stick typically must travel several times its length to reach the melt plate. The wax-like components from which phase change ink sticks are typically made are typically designed to bond to media of many different types, and, accordingly, they may become slightly sticky in some environmental conditions. Consequently, some phase change ink printers occasionally encounter intermittent sticking and slipping of ink sticks in the ink loaders as the ink sticks are pushed through the ink loaders. Ink loader length and complexity of the feed path may also contribute to the intermittent sticking of ink sticks in the feed channel.
FIG. 2 is a simplified cross-sectional view of a prior art feed channel 60 and a phase change ink stick 24. In channel 60, an additional support 64 protrudes from the lateral side that is opposite the lower offset features 68. The support 64 helps reduce the opportunity for intermittent sticking by enabling gravity to cause the ink stick 24 to pivot somewhat (e.g., as indicated generally by the arrow 72) about the lower laterally offset features 68 and slidably lean against the side rail feature 64. While side rail features, such as support 64, have worked reasonably well to properly position and orient ink sticks 24 in their path to a melt plate, sometimes reverse pivoting or other dislodging of the ink sticks 24 occurs when a printer is moved or jostled during normal use. These actions may result in misalignments of the ink sticks 24 that can lead to misalignment of the ink sticks in the feed channel and impact their progress down the feed channel. Leaning may also result in side loads in the lower guides that may amplify sticking issues arising from friction between the phase change ink sticks and the guides.
As emerging technologies reduce the time for generating solid ink images, faster solid ink delivery systems must be developed. Increased speed, however, may increase the risk of intermittent sticking. One proposed solution is to widen the phase change ink sticks to increase melt surface areas to generate more ink as an ink stick is melted. Increasing the size of the ink sticks may result in greater size tolerances for manufacturing the ink sticks and for construction of the corresponding ink loaders. These increased tolerances may lead to larger clearances between the ink sticks and corresponding ink loader guide features. These enlarged clearances could allow undesirable skewing and jamming of the ink sticks in some ink loaders, especially with ink sticks widened so their width-to-length ratios (“aspect ratios”) become disadvantageous. Therefore, enhanced control of ink sticks as they move through a feed channel is desirable.
Solutions to these issues encountered with the feeding of solid ink sticks to a melt plate through a feed channel are provided by the ink stick configurations disclosed in the two co-pending patent applications cross-referenced above. These ink stick configurations interact with anti-skewing features in the feed channels to maintain proper orientation of the ink sticks in the feed channel. The anti-skewing features, such as side rails that extend into side slots in the ink sticks, cannot extend into the loading area for the ink sticks when the insertion direction is generally orthogonal to the feed channel. If they did, they would engage the bottom of the ink stick and prevent it from dropping onto the bottom support extending from the channel.